1. Field of the Invention
The present invention relates generally to a utility knife and methods of making such a knife. More particularly, the present invention relates to an improved utility knife with features to improve functionality and safety.
2. Description of the Related Art
Those concerned with the art are desirous of making a utility knife which is inexpensive, safe, versatile, and rugged. Further, it is desirable to provide a utility knife which reduces or prevents damage to the contents of cardboard boxes opened with the knife, and which is durable and easy to use. Optimally a utility knife is easily grasped and provides a secure grip, safety and certainty in its use, even while the user's hands are moist and slippery. It is desirable that a utility knife reduce the fatigue inherent in strenuous and hard cutting in which such knives are used. Further, practitioners in the art desire to provide a knife that can be manufactured at reasonable cost and which will provide convenience in the use and maintenance, which is aesthetically pleasing and comfortable to hold, and which is as safe as possible, given the inherently dangerous nature of the device and its customary uses. It is also desirable to provide for safe and convenient storage of spare knife blades within the utility knife itself.
For example, U.S. Pat. No. 3,192,624, issued to D. Gringer, teaches a utility knife in which a handle has a forward longitudinal cavity in which a blade carrier member is slidably received. The disclosed knife has a rear cavity in which a number of spare blades are received. The blade carrier member carries a double-ended cutting blade, and is movable longitudinally within the forward cavity between a retracted safety position wherein the blade is entirely within the handle, and an extended operating position where a triangular end part of the blade extends forwardly out of the handle. The handle is vertically split and includes two portions which are almost mirror images of one another. A screw secures the two handle portions together, and allows their separation with the use of a screwdriver. This separation allows reversal of the cutting blade and substitution of one of the unused spare blades for a used cutting blade.
A similar utility knife is presented in U.S. Pat. No. 3,879,847, issued to D. Roll, in which blades may be changed without disassembly of the handle by forward extension therefrom of a forward part of a channel-like blade carrier member. As the Roll disclosure points out, his utility knife avoids the inconvenience of carrying a screwdriver with which to open the handle of prior utility knives. However, his knife does not offer the convenience of spare blade storage in the knife handle.
Another type of utility knife is represented by German Patent No. 531,248, and descendants of the disclosed design. This type of utility knife includes a flattened tubular handle, with a blade carrier slidable in the handle between a retracted position, sheathing the blade entirely in the handle, and an extended operating position, in which part of the blade is exposed forwardly of the handle. A spring-arm part of the blade carrier includes a lug receivable in spaced-apart notches incorporated in the handle to retain the carrier in selected positions, including a retracted position and various positions of blade extension. A button is secured to the spring arm for disengaging the lug from the notches and moving the blade carrier to a selected position.
Variations within this design type include differing handle designs, differing means of securing the blade carrier in position, and the use of differing types of blades. For example, a common single-edge razor blade is a favored blade for many of these prior utility knives, although it has many deficiencies in such use. Such a razor blade is brittle, thin, and not very rugged. Consequently, a razor blade may break off if a large or repetitive twisting or bending force is imposed on the blade in use. Certain other of these knives use a trapezoidal-shaped double ended all-purpose (AP) blade, which is considerably more rugged than a razor blade.
U.S. Pat. Nos. 2,840,903, 3,195,231, 3,525,152, 3,621,570 and 4,570,342 may be considered as representative design descendants of German Patent No. 531,248 discussed above. Generally, this type of knife is made with a handle of folded sheet metal. The handle has a rather small edge radius due to this construction. These knives are relatively thin, and provide only a small handle edge surface area against which manual cutting pressure may be exerted. This small handle edge radius and small edge surface area can combine to make many of these knives quite uncomfortable to use, especially in hard cutting. Even when the user is wearing gloves, some of these knives are so thin that an uncomfortable pressure groove is often formed in the user's hand during hard cutting work. Users may then find themselves shifting the knife in their hand to avoid the sensitive pressure groove, and in the process may be found attempting to use the knife in a less than optimum grip position. Understandably, this kind of incorrect use may contribute to fatigue and injuries. Especially in hard use, the thin, fragile, or difficult to control knives of the above-described category are generally recognized as having limitations in applications to which they can be put.
A further variation of utility knife design is represented by knives specially adapted for opening cardboard cartons or boxes. In this use, the carton is generally held in front of the user with one hand and arm, and is cut by drawing the knife with the other hand toward the user across the side wall of the carton. Because such use in a commercial setting frequently involves the need for speedy work, and cardboard does present considerable resistance to cutting, flesh wounds are common. For example, sometimes, as a result of insufficient care by a user, the knife blade springs free at the end of a cut and catches the user's arm. In the design of knives for this use, particular attention must be given to protecting both a user of the knife, and the contents of a cardboard carton to be opened, from inadvertent cuts.
U.S. Pat. No. 3,178,812, issued to A. J. Lurie, discloses a utility knife having a pair of spaced-apart plate-like blade guards. One guard is for inside, and the other for outside, of a carton. The inner guard is to protect the carton contents during cutting of the carton sidewall, and is carried at the end of a hook-like extension of the handle. This type of utility knife presents at least some inconvenience in use because of the necessity to provide for entry into the carton of the inner plate-like guard.
A similar hook-like guard is disclosed in U.S. Pat. No. 4,167,810, issued to R. Gilbert. The Gilbert reference also discloses protecting the contents of a carton from the blade while the carton is opened. A hard point is provided for punching a hole in the carton for subsequent insertion of the hook-like guard.
An alternative form of blade guard, in this case for protecting the user, is seen in U.S. Pat. No. 4,675,996, issued in 1987 to T. DuBuque. The Dubuque disclosure teaches a pair of spring-loaded pivotal guard plates secured to the handle of the knife to prevent accidental exposure of the blade edge. The guards taught are stated to pivot and expose the blade edge when the knife is drawn along the side of a carton. Why these pivotal guard plates would not also pivot away to expose the blade if the knife were inadvertently drawn across the user's arm, for example, is not clear from the patent. Some mitigation of the danger of inadvertent cutting of the user is contemplated by the disclosure however.
A further alternative form of blade guard, for protecting both user and carton contents, is disclosed in U.S. Pat. No. 4,744,146, issued to the present inventor named herein. In my knife design disclosed in that reference, a plate-like guard member lies parallel and adjacent to, but spaced apart from, the blade in its extended position. The plate-like guard member provides a guide surface by which the knife may be guided along the top corner of a carton to be opened while the carton side wall is cut to remove the carton top. Because the edge of the blade is recessed behind the edges of the guard plate, a user of the knife is less likely to be cut with the knife. Also, the blade penetrates the side wall of the carton to a controlled distance in a location immediately adjacent to a top inside surface of the carton. Consequently, the contents are less likely to be damaged by the blade. The knife design disclosed also offers improved purchase and ease of use. This is because the handle is formed of a sturdy aluminum extrusion offering a considerably larger surface area against which cutting pressure can be applied by a user of the knife, as well as comfortable rounded outer edge surfaces of relatively large radius. This prior knife design also includes features which help avoid accidental dropping of the worn blade when blade replacement is necessary, and provides for storage of several spare blades within the knife handle.
A similar guard member is seen in U.S. Pat. No. 5,054,198, issued to R. Gmoch. The disclosure of that reference differs from my prior design in several ways, but so far as the guard feature is concerned, it differs with regard to an angular relationship between the guard and the cutting blade.